Carpet underlay



July 20, 1965 Filed Aug. 29, 1962 (PRIOR ART) I 40 KT 0 WWW]W" q lulufllumlfiii FIG. 5 (PRIOR ART) INVENTOR. THOMAS FRANKLIN C BY PETERSON United States Patent 0 3,196,315 CARPET UNDERLAY Thomas F. Peterson, Shaker Heights, Ohio Filed Aug. 29, 1962, Ser. No. 220,241 6 Claims. (11. 317-2) The present invention pertains to the art of carpet underlay and more particularly to an improved carpet underlay of the type used to form a resilient cushion under a carpet.

The invention is particularly applicable to a sponge rubber carpet underlay and the invention will be discusse with particular reference thereto; however, it will be ap preciated that the invention has much broader applica tions and may be used in carpet underlay constructed of various materials either sponge, or non-sponge, and either coated onto the underside of a carpet or formed as a separate sheet to be positioned under a carpet.

Under conditions of low humidity, especially in winter, carpeting becomes dry and accordingly has a very high electrical insulating value. As a person walks over the dry carpeting and rubs the carpeting with his shoes, electrons from the shoes are deposited onto the carpeting and the persons shoes exhibit a lack of electrons. Accordingly, a charge is created on the person, and, as this charge on the person is separated from the equal, but opposite, charge on the carpeting, work is done which increases the potential, or voltage, between the person and the carpeting. This action can build up a voltage on the person of several thousand volts which is a sufificient voltage to develop a spark whenever the person comes within the vicinity of a grounded conductor. Irrespective of the electrical explanation of the phenomenon of static electricity, it is commonly known that a person walking over a carpet, during times of low humidity, generates a sparking voltage which is discharged when the person touches a grounded object. This generation of a sparking voltage on the person is not only annoying, but it is also dangerous, since the spark caused by the high volt age may cause explosions, fires and the like.

The hazards and annoyances surrounding the genera tion of the sparking voltage as a person traverses a carpeting have been long recognized. Various proposals have been made for their elimination and, heretofore, these proposals have depended on making the upper surface of the carpeting electrically conductive by incorpo rating into the tufts or matting or" the carpeting a number of conductive elements which extended through the can peting into an electrically conductive sheet under the can peting. This conductive sheet under the carpeting was grounded so that the elements protruding upwardly through the carpeting would be at ground potential. Accordingly, any charge on the upper surface of the carpet was dissipated by conducting the charge into the grounded sheet under the carpet. Such obvious proposals, how ever, required that the fabric of the carpeting be specially woven or constructed to include a great number of these conductive elements. Metal wires forming the conductive elements and woven into the carpeting, not only added to the cost, but they were unlike the other material in the carpeting and it was found that these wires tended to wear at a different rate than the carpeting. This caused an unpleasing appearance and was accordingly objectionable. Furthermore, conductive wires extending upwardly through the carpeting tended to corrode or bend downwardly out of engagement with the upper surface of the carpeting and were often completely useless. In these prior attempts to eliminate the sparking problems of certain carpeting, as was previously mentioned, the conductive elements, or wires, extending through the carpeting were connected to a highly conductive, grounded sheet below the carpeting. By this 3, l ,3 l 5 Patented July 20, 1965 arrangement, the upper surface of the carpeting was at ground potential so that a person on the carpet could be seriously shocked when inadvertently touching a high potential source such as found around household electrical appliances. Further, the conductive sheet under the carpeting had to be intimately associated with the conductive elements extending through the carpeting and it was therefore impossible to provide a conveniently removable carpet underlay which could also prevent the generation of a sparking voltage on a person walking over the carpet. If a sponge carpet underlay, of the type now commonly used to form a cushion under a carpet, were to be used with the conductive type of charge dissipator found in the prior art, it was necessary to use a conductive lower sheet to form the connections with the conductive elements extending through the carpeting and a separate sponge rubber underlay. This was too expensive to be commercially feasible.

These and other disadvantages have been eliminated by the present invention which is directed toward a separable carpet underlay which prevents build up of a sparking voltage and is formed from a semi-conductive material without direct electrical contact with the upper surface of the carpeting. The term semi-conductive material as herein used refers to a substance having an electrical resistivity substantially midway in the range between the resistivity of a conductor, such as copper, which resistivity as 1.7x 10- ohms/cm. and the resistivity of an insulator, such as porcelain, which resistivity is 3.O 10 ohms/cm}. Preferably, the resistivity of a semi-conductive material as used herein is substantially Within the range of 10 ohms/cmfi-lO" ohms/ emf. Accordingly, a semi-conductive material is substantially less conductive than a conductor and substantially more conductive than an insulator.

In accordance with the present invention there is provided a carpet underlay formed from semi-conductive resilient or sponge like material having a resistivity substantially in the range of 10 -10 ohms/cmfi.

In accordance with a further aspect of the present invention there is provided, in combination, a carpet having an upper wearing surface, an underlay of resilient sponge like material adapted to form a cushion layer under the carpet, which material has the characteristic of being a semi-conductor wherein the underlay is physically spaced from the wearing surface and forms a capacitive coupling with objects on the wearing surface.

By providing a carpet with a sponge underlay constructed in accordance with the present invention, high potentials are not developed as a person walks over the wearing surface of the carpet and this beneficial feature is obtained without providing either an electrical connection from the underlay to the wearing surface of the carpet or a means for grounding the underlay.

The primary object of the present invention is the provision of a carpet underlay which prevents creation of a sparking potential by a person walking over the carpet and which is inexpensive to construct and easily installed under a carpet without modification of the carpet.

Another object of the present invention is the provision of a floor covering or carpet underlay which prevents creation of a sparking potential by a person on the floor and which covering or underlay is formed of a semiconductive material.

Still another object of the present invention is the provision of an underlay as defined above wherein said underlay comprises a sponge rubber with a coating of semiconductive material thereon.

Yet another object of the present invention is the provision of a carpet underlay of the type defined above wherein the semi-conductive material is formed from blown or whipped sponge rubber having a conductive material dispersed throughout.

Still another object of the present invention is the provision of a sponge rubber carpet underlay formed from a mixture of a sponge rubber material and a conductive material wherein the carpet underlay has a resistivity substantially in the range of 10 -10 ohms/cm.

Another object of the present invention is the provision of a semi-conductive sponge rubber carpetunderlay which prevents creation of a sparking potential on a person walking over the carpet without having electrical conductivity between the upper surface of the carpet and the sponge rubber underlay.

Another object of the present invention is the provision of a semi-conductive sponge rubber carpet underlay which prevents creation of a sparking potential on a person walking over the carpet by creating a capacitive coupling between the underlay and the person.

Still a further object of the present invention is the provision of a semi-conductive sponge rubber carpet underlay which prevents creation of a sparking potential on a person walking over the carpet without forming a short circuit between the upper surface of the carpet and without a ground connection to the carpet underlay.

Another object of the present invention is the provision of a semi-conductive sponge rubber carpet underlay as defined above wherein there are no physical connections between the carpet underlay and the carpet so that the underlay may be easily separated from the carpet without damaging same.

Another object of the present invention is the provision of a semi-conductive sponge rubber carpet underlay which underlay provides an adequate cushion for the carpeting while also preventing the creation of a sparking potential on a person walking over the carpet.

These and other objects and advantages will become apparent from the following description used to illustrate the preferred embodiments of the invention as read in connection with the accompanying drawing in which:

FIGURE 1 is a partial cross sectional view illustrating an embodiment of the invention;

FIGURE 2 is a partial cross sectional view illustrating a modification of the embodiment disclosed in FIG- URE 1;

FIGURE 3 is a partial cross sectional view showing the use of the embodiment of the invention as shown in FIG- URE 2;

FIGURES 4 and 5 are somewhat schematic diagrams illustrating the operation of the prior art; and

FIGURES 6 and 7 are somewhat schematic diagrams showing the operation of the preferred embodiment of the present invention.

Referring now to the drawing, wherein the showings are for the purpose of illustrating preferred embodiments of the invention only and not for the purposes of limiting same, FIGURE 1 shows a carpet underlay A adapted to be positioned under a conventional carpet to provide a cushion for the carpet and comprised of a plurality of uniformly molded bulges 10 and recesses 12 as viewed from the upper surface of the underlay. Carpet underlay having the same general configuration and formed from a blown or whipped sponge material, such as sponge rubber is quite common; however, such a carpet underlay is an electrical insulator and allows creation of high sparking potential on a person walking over the carpet. The present invention is directed toward a carpet underlay that prevents the creation of high sparking potentials and in accordance with the invention, the carpet underlay A is formed from a semi-conductive material. In accordance with the preferred embodiment of invention, the carpet underlay is formed of a blown sponge rubber rendered semi-conductive by the incorporation of conductive carbon particles within the sponge rubber material forming the underlay. The material conventionally used for the sponge rubber underlay usually contains some reinforcing carbon black; however, the amount of carbon black is so small that the conductivity of the rubber is not materially altered and its resistivity normally ranges between 10 10 ohms/ch1 By introducing before vulcanization approximately 35% by weight of conductive carbon black, the resistivity of the unvulcanized rubber stock is reduced to 10' ohms/cm. and by increasing this percentage of carbon black to about the resistivity is further reduced to approximately 10 ohms/cm? Accordingly, by producing the unvulcanized rubber stock with between 35 and 58 percent by weight of conductive carbon black, the resistivity of the unvulcanized material is intermediate between insulation material and an electrical conductive material and, accordingly, the material may be termed semi-conductive.

Although, in accordance with the preferred embodiment of the present invention, conductive carbon black is used in a certain percentage to provide a resistivity in substantially therange of 10 -10 ohms/cm. it is appreciated that various other conductive materials may be incorporated in the material forming the carpet underlay in appropriate proportions to provide substantially the same range of resistivity without departing from the intended spirit or scope of the present invention. Also, it is within the contemplation of the invention to incorporate other material besides rubber as the material used in manufacturing the underlay, For instance, any natural rubher, various forms of synthetic rubbers, and thermosetting and thermoplastic rubber-like materials such as oilmodified phenolic resins, plasticized polymers or copolymers of vinyl esters (as the chloride, acetate, etc.), polymerized styrene and acrylates may be modified by appropriate material to provide a resistivity in the above mentioned range. The conductive carbon particles which may be included within the underlay material are, without limitation, channel black, acetylene black, amorphous graphite and the like. Of course, other types of conductive particles may be incorporated within the underlay material without departing from the intended scope of the invention. When the carbon black in fine particle form is properly dispersed within the material, there is not only developed an electrical semi-conductivity but there are general improvements in the physical properties, such as resistance to abrasion, tearing, etc. In summary, the underlay A is formed from a semi-conductive material having .a resistivity substantially in the range of 10 -10 ohms/cm. and in the preferred embodiment is a sponge rubber structure having dispersed therein conductive carbon particles such as particles of carbon black.

Referring now to FIGURE 2, a modification of the embodiment disclosed in FIGURE 1 is shown wherein a sponge rubber carpet underlay B quite similar to the underlay in FIGURE 1 is provided with bulges 2t and recesses 22 facing upwardly and under surface peaks 26 facing downwardly. Appropriately afiixed onto the under surface peaks 26 is a fabric material C which prevents lateral stretching of the sponge rubber carpet underlay B during use under a carpet. The material used for the carpet underlay C is identical to the material used for the carpet underlay A shown in FIGURE 1.

In FIGURE 3, the carpet underlay B is shown in use wherein a carpet D is positioned over the carpet underlay B so that the carpet underlay provides a resilient cushion for the carpet in the conventional manner. The carpet D is provided with an upper wearing surface 30 and an under surface 32 wherein the under surface rides on the carpet underlay and is non-conductive so that there is no electrical conductivity from the surface 30 to the sponge rubber underlay B. Accordingly, the wearing surface 30 is electrically insulated from the carpet underlay and there are no structural modifications of the carpeting to provide connection of electrically conductive elements with the semi-conductive carpet-underlay B.

In accordance with the invention, the use of a semiconductive carpet underlay produces surprising and unexpected results; for instance, sparking voltage is prevented at surface 3%) with not electrical contact from the carpet underlay to the wearing surface 3% and with not ground connection for the carpet underlay. To illustrate the operation of the carpet underlay constructed in accordance with the present invention, reference is made to FIGURES 4 and 5 which illustrate schematically the suggested manner in which a sparking Voltage is created when the carpet is not provided with a means for preventing a voltage build up between the carpet and a person walking thereon. This description on the generation of static electricity as a person walks over a conventional carpet is not a part of the invention and is only background information used to explain the operation of the present invention. It is appreciated that such a static sparking voltage is created, irrespective of the electrical theory proffered to explain the same. For explanatory purposes, the circular body 4'8 represents a member or person scufiing along the wearing surface 30 of carpet D. Electrons are deposited on the wearing surface 3% and the body 40 is thus rendered positive. The voltage between the surface 30 and the body 49 is not appreciable and will not cause sparks; however, as the body as is moved a substantial distance x the spacing between the electrons deposited on the carpet and the positive charge of body 46 is greatly increased. This reduces the capacitance and correspondingly increases the voltage. This increase in voltage causes a spark discharge as the body 4t) approaches a member having a substantially lower potential. The electrons on the surface of the carpeting D cannot move along with the body 40 because the carpet does not form a conductive path.

A sponge rubber carpet underlay constructed in accordance with the present invention, not only provides a cushion for the carpet D, but also, prevents the build up of voltage on body 4% by a capacitor coupling arrangement illustrated in FIGURES 6 and 7. As the body 40 scuffs along the surface 30, electrons are deposited which makes the body 40 positive and the surface 33 negatve. Since the carpet underlay B is semi-conductive, the electrons on the upper surface of the rug cause the underlay to be positive directly beneath the deposited electrons, and accordingly, the carpet underlay has freed the moving electrons shown in FIGURE 6 as a. These electrons at can follow through the carpet underlay to any position adjacent the body 40. Accordingly, there is no substantial change in the distance between the positive and negative members and no substantial voltage build up is realized. A carpet underlay constructed in accordance with the present invention, does not differ in appearance from the conventional carpet underlay and may be used as conviently as known carpet underlay with the added benefit that the possibility of creating high sparking potentials is eliminated. The principle of operation of the present invention does not require electrical conductivity between the wearing surface 30 and the carpet underlay because the capacitive coupling of the carpet underlay does not require conductivity of the electrons to a grounded position. Further, because the carpet underlay is electrically semiconductive, there is no chance of having a high current discharge through a person on the upper surface of the carpet as he touches a defective electrical appliance. If the carpet underlay required electrical conductivity between the upper surface 30 and the carpet undelay for its operation, there would be a tendency to ground a person walking over the surface of the carpet.

While the various forms of rubber and resinous material can be modified into semi-conductive materials as described, some special additional steps may be necessary for certain materials. For instance, it has been observed that thermoplastic vinyl polymer or copolyrner materials do not yield satisfactory semi-conductivity merely by the physical incorporation of carbon particles, because of the tendency of these polymers to return to their original shape upon subsequent heating and cooling. To correct this problem, the polymers are subjected to a sufficiently high temperature and pressure such as to release the strains in them that cause the tendency to distort and thus interfere with the semi-conductivity. This can be accomplished, for example, in a calendering operation upon a sheathing or rough backing with Vinylite (copolymer of vinyl chloride with a small percentage of vinyl acetate) or Koroseal (polymerized vinyl chloride (by heating to temperatures of the order of 300 F. and applying high pressures; it is then found that the semi-conductivity and physical properties are retained in subsequent heating of the material.

In further defining the scope of the present invention, it is to be appreciated that, in accordance with another aspect of the invention, sponge carpet underlay A may be converted into a semi-conductive element by applying a coating of semi-conductive material on one surface of underlay A. Such a material could be a latex base cement having dispersed therein a conductive material in sufficient quantity to form the cement into a semi-conductive material as the term is herein defined.

The present invention has been discussed in conjunction with certain structural embodiments; however, it is to be appreciated that various structural changes may be made without departing from the intended spirit and scope of the present invention.

Having thus described my invention, I claim:

1. In the combination of a carpet formed from an electrical insulating material and having an upper wearing surface and a lower support surface, said surfaces being electrically insulated one from the other, and a carpet underlay forming a cushion beneath said carpet, the improvement comprising: said carpet underlay being formed from a mixture of sponge, rubber-like material and a sufficient amount of electrically conductive material to make the resistivity of said mixture substantially within the range of 10 -10 ohms/cm. whereby said carpet forms a capacitance coupling between said upper wearing surface and said underlay without an electrical connection from said wearing surface to said underlay.

2. The improvement as defined in claim 1 wherein said electrically conductive material is carbon particles.

3. The improvement as defined in claim 2 wherein said mixture comprises 35%- 50% by weight of said carbon particles.

4. In a carpet underlay formed from a sponge, rubberlike insulation material and having on the lower surface thereof a series of molded downwardly facing bulges and upwardly extending recesses forming a generally rippled downwardly facing support surface, the improvement comprising: said sponge, rubber-like material including a sufficient amount of electrically condutcive material to make the resistivity of said underlay substantially within the range of 10 -10 ohms/cmfi.

5. The improvement as defined in claim 4 wherein said underlay has a lower reinforcing fabric material coextensive with said support surface, said material extending between said bulges and secured thereto to prevent lateral stretching of said rippled support surface.

6. The improvement as defined in claim 4 wherein said electrically conductive material is carbon particles.

References Cited by the Examiner UNITED STATES PATENTS 2,302,003 11/42 CadWell et al. 3l72 2,597,741 5/52 Macy.

2,845,962 8/58 Bulgin 3l72 3,034,942 5/62 Heiks 16167 3,035,955 5/62 Zucker et al. 3 17-2 SAMUEL BERNSTEIN, Primary Examiner. 

1. IN THE COMBINATION OF A CARPET FORMED FROM AN ELECTRICAL INSULATING MATERIAL AND HAVING AN UPPER WEARING SURFACE AND A LOWER SUPPORT SURFACE, SAID SURFACES BEING ELECTRICALLY INSULATED ONE FROM THE OTHER, AND A CARPET UNDERLAY FORMING A CUSHION BENEATH SAID CARPET, THE IMPROVEMENT COMPRISING: SAID CARPET UNDERLAY BEING FORMED FROM A MIXTURE OF SPONGE, RUBBER-LIKE MATERIAL AND A SUFFICIENT AMOUNT OF ELECTRICALLY CONDUCTIVE MATERIAL TO MAKE THE RESISTIVITY OF SAID MIXTURE SUBSTANTIALLY WITHIN THE RANGE OF 10**3-10**7 OHMS/CM.3 WHEREBY SAID CARPET FORMS A CAPACITANCE COUPLING BETWEEN SAID UPPER WEARING SURFACE AND SAID UNDERLAY WITHOUT AN ELECTRICAL CONNECTION FROM SAID WEARING SURFACE TO SAID UNDERLAY. 